The present invention relates to an optical receiver for receiving alternating-light data signals and for storing electrical energy obtained from extraneous light, having a photodiode for receiving light and for converting the light into a photocurrent. The received light comprises extraneous light and an alternating-light data signal component having a higher frequency in comparison to the extraneous light, which is generated by a light source emitting a data signal. The photocurrent resulting from the conversion of the light comprises a data signal current and an extraneous light current.
The invention also relates to an optoelectronic measurement arrangement having an extraneous light compensation comprising a data signal light source and a compensation light source, an optical receiver with a photodiode and an amplifying unit and an extraneous light compensation circuit. The invention further relates to a method for storing electrical energy obtained from extraneous light, and for receiving optical alternating-light data signals.
Optical sensors receive light, which in addition to the actively emitted light of a data signal light source also comprises the extraneous light prevailing in the environment, in particular the daylight. The received ambient light is in general substantially more intense than the light component radiated by the data signal light sources (useful signal light source).
Optical receivers of this kind are used for example as parts of active optical sensors, which in addition to the receiver also comprise a light source and emit light. The light emitted by the optical sensors is reflected at “illuminated” objects and after reflection received, whereby information on these “illuminated” objects can be obtained. Since the component of the ambient light here also is significantly greater than the data signal light component, the sensors are e.g. screened and shaded in such a manner that as little ambient light as possible reaches the optical receiver. A different path is taken by optical sensors that have an extraneous light compensation circuit. Such optical sensors or optical receivers are known, for example from the following applications:
EP 0 706 648 A1DE 101 33 823DE 28 49 186DE 103 00 223 A1
The ambient light does not contain any useful information for the analysis of the data signal, in particular for detection of distant objects and/or their positions. Due to the high light intensity, a high photocurrent level is produced in the photodiode of the receiver, which would drive the receiver amplifier of this type of sensor into saturation. Therefore, the extraneous light or ambient light component of the photocurrent is suppressed before the data signal component of the photocurrent is amplified. In doing so, the fact that the ambient light is lower-frequency than the data signal is exploited. For example, the light produced by artificial lighting often has a frequency of 50 Hz or 60 Hz and harmonics thereof. The natural ambient light, or sunlight, leads to a DC component in the photocurrent.
In optical receivers the photodiode is often biased in the reverse direction, whereby in the simplest case the photocurrent is dissipated via a resistor to the power supply. This has the disadvantage however that due to this type of circuit, the photocurrent increases the power consumption of the entire circuit, since the reverse-biased photodiode works not as a source, but as a “sink” and the photocurrent component produced by the ambient light must be generated by the power supply.
In order to minimize any loading of the power supply by the photocurrent produced by the ambient light, it has proved advantageous therefore to operate the photodiode in the forward-biased direction. When connected in this manner, the power supply of the sensor at least is not under load.
EP 1 956 493 A1 describes am optical interface module with which data and energy are transmitted from a computer to an external device. The energy is supplied via actively emitted light that is transmitted via an optical fiber and then subsequently converted back into an electrical signal. By means of a signal separator, the data signal is decoupled from the energy signal. The energy, very sharply focused, strikes a special optical energy transducer, which delivers an output voltage of at least 5.5 V. However, an energy transducer of this kind with a small receiving area is a very expensive and complex element to produce, which costs several times more than conventional photodiodes. In order for sufficient energy to be transmitted, cable-bound optical energy transmission must be used. In addition, generating the optical energy signal is laborious and requires a power laser. Only in this manner can sufficient energy be transmitted so that the signal separator, in the form of a Schottky diode and a downstream storage capacitor, can be supplied. The disadvantage remains however that due to the Schottky diode, the output voltage drops by approximately 0.4 V.
In EP 0 367 333 A1, an infrared remote control unit is described which transmits data signals in the form of infrared light. At the same time the remote control unit is intended to receive energy from the ambient light in order to provide energy support for the batteries of the remote control unit. For this purpose a plurality of photodiodes are connected in series to be able to generate an output voltage which is required for charging the battery.